Mode-locked fiber laser having an optical path length controller for a fiber resonator

Abstract

The pulse repetition frequency of an optical pulse generator built with a fiber laser (LAS) is synchronized to a fixed clock frequency (fc). The synchronization is accomplished via means (M) for changing the optical path length of the resonator (RES), which is controlled by a signal from a control device (RE). The criterion for the synchronization is the effective value of an interference signal superimposed on the signal light, which increases with increasing deviation of the pulse repetition frequency from the clock frequency. A portion of the output signal (A) of fiber laser (LAS) is optically/electrically converted by the control device (RE), and the effective value of the interference signal is determined by filtering and rectifying the electrical signal obtained in this manner. After subsequent amplification and regulation, the control signal for the means (M) to change the optical wavelength is obtained. The control signal is additionally modulated with a wobble signal, so that the pulse repetition frequency always varies around the optimum value and is synchronized in this way.

What is claimed is: 
     
       1. A mode-locked fiber laser (LAS) for generating a pulsed light signal of a predetermined pulse repetition frequency, comprising a fiber resonator (RES), a means (M) for changing the optical path length of the fiber resonator (RES), and a control device (RE) which is connected to the fiber resonator (RES) and to the means (M) for changing the optical path length and in which a control signal for the means (M) for changing the optical path length is generative from a portion of an output signal of the mode-locked fiber laser (LAS), characterized in that in the control device (RE), an interfering signal superimposed on the pulsed light signal is determinable whose frequency is lower than the predetermined pulse repetition frequency, and   the control signal is derivable from the interfering signal.   
     
     
       2. A mode-locked fiber laser (LAS) as claimed in claim 1, characterized in that the control device (RE) contains an optical-to-electrical transducer (OE), a detector (DET), an amplifier (AMP), and a controller (PI), that in the detector (DET), the root-mean-square amplitude of the interfering signal is determinable, and that the control signal for the means (M) for changing the optical path length is derivable from the root-mean-square amplitude. 
     
     
       3. A mode-locked fiber laser (LAS) as claimed in claim 2, characterized in that the amplifier (AMP) is a phase-sensitive amplifier, and that the control signal is modulated (fw). 
     
     
       4. A mode-locked fiber laser (LAS) as claimed in claim 1, characterized in that the fiber resonator (RES) is a ring resonator. 
     
     
       5. A mode-locked fiber laser (LAS) as claimed in claim 1, characterized in that the laser is an actively mode-locked fiber laser.